Embodiments of the invention relate generally to diagnostic imaging and, more particularly, to an apparatus and method for magnetically controlling an electron beam (e-beam).
X-ray systems typically include an x-ray tube, a detector, and a support structure for the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation typically passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then emits data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. One skilled in the art will recognize that the object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in an x-ray scanner or computed tomography (CT) package scanner.
X-ray tubes include a rotating anode structure for the purpose of distributing the heat generated at a focal spot. The anode is typically rotated by an induction motor having a cylindrical rotor built into a cantilevered axle that supports a disc-shaped anode target and an iron stator structure with copper windings that surrounds an elongated neck of the x-ray tube. The rotor of the rotating anode assembly is driven by the stator.
An x-ray tube cathode provides an electron beam that is accelerated using a high voltage applied across a cathode-to-anode vacuum gap to produce x-rays upon impact with the anode. The area where the electron beam impacts the anode is often referred to as the focal spot. Typically, the cathode includes one or more cylindrical or flat filaments positioned within a cup for providing electron beams to create a high-power, large focal spot or a high-resolution, small focal spot, as examples. Imaging applications may be designed that include selecting either a small or a large focal spot having a particular shape, depending on the application. Typically, an electrically resistive emitter or filament is positioned within a cathode cup, and an electrical current is passed therethrough, thus causing the emitter to increase in temperature and emit electrons when in a vacuum.
The shape of the emitter or filament affects the focal spot. In order to achieve a desired focal spot shape, the cathode may be designed taking the shape of the filament into consideration. However, the shape of the filament is not typically optimized for image quality or for thermal focal spot loading. Conventional filaments are primarily shaped as coiled or helical tungsten wires for reasons of manufacturing and reliability. Alternative design options may include alternate design profiles, such as a coiled D-shaped filament. Therefore, the range of design options for forming the electron beam from the emitter may be limited by the filament shape, when considering electrically resistive materials as the emitter source.
Electron beam (e-beam) wobbling is often used to enhance image quality. Typically, wobble is achieved using electrostatic e-beam deflection. However, higher image quality can be achieved by using magnetic deflection. Wobbling via magnetic deflection may achieve a high image quality by ensuring that the electron beam moves from one position to the next usually as quickly as possible while staying in the desired position without straying. However, known systems that perform magnetic wobbling use complex topologies that often include bulky and expensive high voltage parts and do not achieve the fast and stable magnetic wobbling desired for enhanced image quality. Because each x-ray tube is not manufactured identically, wobble may differ from tube to tube. Further, adjustments to the magnitude of wobble in such systems is difficult to control.
Therefore, it would be desirable to develop an apparatus and method for magnetic deflection that overcomes the aforementioned drawbacks and achieves fast, stable, and adjustable e-beam magnetic control.